Embodiments of the inventive concept relate generally to touch sensing technology. More particularly, embodiments of the inventive concept relate to capacitive touch sensors and devices incorporating the capacitive touch sensors.
A touch sensor is a device that detects the presence of an object such as a finger or stylus within a designated input area. One common form of touch sensor is a touchscreen that senses the presence and position of a finger or stylus on a visual display. Such touchscreens can be found in a wide variety of electronic devices such as automated teller machines, home appliances, televisions, cellular phones, portable media players, personal digital assistants, and e-books, to name but a few.
Touchscreens come in a variety of different forms, including resistive touchscreens, surface acoustic wave touchscreens, infrared touchscreens, and capacitive touchscreens.
A resistive touchscreen comprises multiple layers of resistive material formed on a substrate such as a glass plate or a transparent plastic plate. Where an object comes in contact with the resistive touchscreen, it changes an electric current across one or more of the layers, and the change of current is used to detect a touch event.
A surface acoustic wave touchscreen comprises an ultrasonic wave generator that transmits ultrasonic waves across a surface of the touchscreen. Where an object approaches the surface of the touchscreen, portions of the ultrasonic waves are absorbed or deflected, allowing a touch event to be detected.
An infrared touchscreen comprises light emitting diodes (LEDs) that create infrared beams across a surface of the touchscreen, and photodetectors that detect the beams. Where an object approaches the surface of the touchscreen, the photodetectors detect interruption of some of the infrared beams. The pattern of interrupted beams allows the infrared touchscreen to detect a touch event.
A capacitive touchscreen comprises an insulator such as glass, and a transparent conductor such as indium tin oxide (ITO) formed on the insulator. Where an object such as a finger touches the capacitive touchscreen, it distorts an electrostatic field of the conductor, which can be measured as a change in capacitance. The change of capacitance is used to detect a touch event.
Among existing touchscreen technologies, resistive touchscreens are among the most common because of their relatively low price. One drawback of resistive touchscreens, however, is that they typically can sense only one touch event at a time. Accordingly, as research is conducted on multi-touch user interfaces, capacitive touchscreens are gaining popularity.